In a typical refrigeration system the flow of refrigerant is often controlled through a series of valve groupings. These valve groups (a.k.a. valve trains) consist of individual valves piped together either through bolted flanges, or weld sections of pipe. These valve trains can be made up of any one of a number of different valve types. One such common train consists of a hand valve, solenoid valve, and a check valve coupled together in series. The direction of the refrigerant flow through the valves is the same order as the valves are listed above. The hand valve is used during service situations of the solenoid and check valves. Upon closure of the hand valve all flow of refrigerant is stopped, allowing the solenoid and check valves to be disassembled and serviced. The solenoid valve provides automatic on/off control of the flow of refrigerant during normal operation. The check valve prevents any reverse flow of refrigerant through the solenoid valve.
A prior art solenoid valve 110, model S4W available from Parker Hannifin Corporation, is shown in FIG. 1. In the S4W valve 110, high pressure liquid or gas is stopped at the inlet passageway side 26′ of the valve 110 by piston 40′. The design of the main piston plug 40′ allows inlet pressure to the internal surfaces of the piston 40′ and to the top of the piston thus holding the valve closed tightly. The internal portions of the piston are open directly to the inlet flow while pressure to the top of piston is gained through a small bleed hole in the piston (not shown).
To open the valve 110, a coil (not shown) on the valve is energized opening a passage (formed by the combination of 52′+54′+38′) which allows the pressure contained on top of the piston 40 to bleed off to the outlet (low pressure) passageway side 28′ of the valve 110. The pressure difference across the piston 40 (low on top/high internally) allows the spring 62′ to be overcome and the higher inlet pressure to push the main valve piston open—thus opening the valve and allowing flow underneath piston and through the valve seat 30′. The valve remains in the open position as long as the coil is energized. Once the coil is de-energized the pressure on top of the piston 40 can no longer bleed to the outlet side of the valve. This causes the pressure on top of the piston to equalize with the pressure in the internal portions of the piston. Equalization is accomplished through the small bleed hole in the top of the piston (not shown). Once the pressure has equalized, the main valve spring 62′ can now push the piston 40′ closed shutting off the valve port 30′. Once again a pressure difference is created between the inlet side 26′ of the valve, and the outlet side 28′ of the valve, helping to hold it shut tightly.
Pilot operated solenoid valves only work in one direction. Should a higher pressure build on outlet side of the valve than on the inlet side, the main piston will be pushed open allowing backward flow through the valve. Thus the need for a separate check valve, such as the prior art CK-1 check valve 210 available from Parker Hannifin Corporation, as shown in FIG. 2. Note that the body is reversed with respect to the flow direction.